The shoe straightening devices to which the present invention relates are commonly known as shoe trees. Shoe trees are generally of two types: the well-known internally applied shoe tree which fits within a shoe and is expanded; and the lesser known type of shoe tree that is applied externally to footwear. Shoe trees in general are used for preventing shoes, as well as boots and other articles of footwear, from losing their shape and becoming creased. As used hereafter, the term "shoe tree" is meant to encompass such devices that are applied to shoes, boots and other articles of footwear.
Shoe trees that are applied internally have two significant disadvantages compared to externally applied shoe trees. One disadvantage is that the internally applied shoe tree operates by pressing the material of the shoe outwardly in order to uncrease it. The shoe upper thus becomes stretched over time. A second significant disadvantage of internally applied shoe trees is the inherent difficulty in applying the shoe tree in a boot. Most internally applied shoe trees simply cannot be made to "turn the corner" in passing from the vertical length or shank of the boot to the horizontal sole portion, or can only do so with great difficulty.
External shoe-trees are generally of universal application to any kind of footwear since they are applied to the outside of the footwear. The external shoe tree also does not distend the footwear upper, since it primarily acts to straighten the sole of the shoe to remove creases. External shoe trees are represented by U.S. Pat. No. 1,106,465 and U.S. Pat. No. 2,266,258, for example.